What the tester is checking
The MOT covers around 70 items grouped into 10 main categories. Not every item gets the same level of scrutiny. Some are a straight pass or fail. Others are assessed for degree of wear or damage, with the outcome depending on how serious that wear is.
Lights and signalling. Headlights, brake lights, indicators, hazard lights, rear fog light, number plate light, and reversing lights where fitted. Each must work correctly and be properly aligned. Broken or missing bulbs are the single most common reason for a fail, and among the cheapest items to fix before the test.
Brakes. The footbrake is tested for performance using a roller brake test. Pads and discs are checked for condition. The handbrake must hold the vehicle on a gradient. Brake fluid is visually inspected but not chemically tested. Uneven braking performance across an axle is a fail.
Tyres. Tread depth must be at least 1.6mm across the central three-quarters of the tyre width and around the full circumference. Condition is also assessed: bulges, cuts, or damage that exposes the ply beneath is a fail regardless of tread depth. Tyres must be the correct size for the vehicle. The spare tyre is not tested.
Steering and suspension. The tester checks for excessive play in the steering wheel, correct operation of power steering where fitted, and the condition of suspension components including shock absorbers, springs, and ball joints. Worn bushes or excessive movement in any joint will fail.
Bodywork and structure. Sharp edges or projections that could injure a pedestrian or other road user are a fail. Corrosion in load-bearing structural areas (floor pan, sills, chassis members) is assessed carefully. Surface rust on bodywork panels is not a fail. Structural rust that compromises the integrity of the vehicle is.
Windscreen and wipers. Damage in the driver's direct field of view (roughly an A4-sized zone in front of the driver) is a fail. A chip or crack outside that zone may result in an advisory rather than a fail. Wipers must clear the screen effectively across both blades. Washer fluid is checked but is not a fail item if empty.
Seatbelts. Every belt fitted to the vehicle must be checked, including rear belts. Each must be in good condition, lock correctly under sharp force, retract smoothly, and be securely anchored at all attachment points. A frayed webbing, a belt that does not lock, or a damaged buckle will fail.
Emissions. Petrol and diesel vehicles are tested differently. Petrol vehicles are assessed using a gas analyser measuring carbon monoxide, hydrocarbons, and the air-fuel mixture. Diesel vehicles are tested using a free-acceleration smoke test: the engine is revved sharply and exhaust opacity is measured. Vehicles first registered before August 1975 are exempt from emissions testing. Removing or bypassing a catalytic converter or diesel particulate filter is an automatic fail.
Horn. Must work when pressed. The sound must be continuous, not intermittent. That is the full extent of the horn test.
Number plates. Must be present front and rear, correctly lit, legible at the required distance, and in the correct format for the vehicle's age. Plates with non-standard fonts, tinted or reflective backgrounds, or missing characters are a fail.
Pass, advisory, and fail: what each result means
| Result | What it means | Can you drive away? |
|---|---|---|
| Pass | Vehicle meets the minimum standard for roadworthiness. | Yes. |
| Pass with minor defect (advisory) | Vehicle passes, but the tester has flagged an item worth monitoring or fixing before the next test. | Yes, but act on it before it becomes a fail. |
| Major defect (fail) | A significant fault affecting safety or emissions. The vehicle cannot legally be driven on public roads. | No. Must be repaired and retested. |
| Dangerous defect (fail) | An immediate road safety risk. The vehicle should not be driven at all. | No. Arrange collection or recovery. |
Minor, major, and dangerous: the 2018 categories explained
In 2018, the DVSA replaced the old binary pass/fail system with a three-tier defect classification. The distinction matters in practice.
Minor defect. Does not affect vehicle safety or have a significant environmental impact. Recorded as an advisory on a passed certificate. You are not legally required to act immediately, but the advisory is telling you something is wearing or deteriorating and will need attention.
Major defect. Affects vehicle safety, has an adverse environmental impact, or puts other road users at risk. This is a fail. The vehicle cannot be driven on public roads until repaired and retested.
Dangerous defect. A direct and immediate risk to road safety. Also a fail, but the vehicle should not be driven at all. Not even to a repair garage. If you receive a dangerous defect fail, arrange collection or recovery rather than driving away.
Most fails in practice are major defects. Dangerous defects tend to involve steering failures, severe brake deficiency, or structural damage severe enough to affect the vehicle's crash protection.
What to do with an advisory
An advisory is not an instruction to act immediately. Your vehicle has passed and is road legal.
What it is telling you is that something is on its way to becoming a fail. Tyre wear approaching the legal limit, brake pads getting thin, or suspension wear starting to show are all typical advisories. They are normal on older vehicles. Ignored year after year, small problems become expensive ones.
The sensible response: get a quote, understand the timescale, and decide whether to fix it now or before next year's test. If the advisory involves something safety-critical (brakes, steering, or tyres), act sooner rather than later.
If your car fails
The garage must give you a VT30 (a refusal of MOT certificate) listing every item that caused the fail. You are entitled to a copy.
You do not have to have the repairs done at the same garage. The tester cannot pressure you to use their workshop. Take the VT30, get quotes elsewhere if you want to, and return wherever makes sense.
If you bring the repaired vehicle back to the same garage within 10 working days, a partial retest covers only the failed items at a reduced fee. Go elsewhere, or wait longer than 10 working days, and you pay for a complete new test.
One point worth being clear on: a vehicle with a major defect fail must not be driven on public roads, but can be driven directly to a pre-booked repair appointment or back to your garage. A vehicle with a dangerous defect should not be driven at all. If you are not certain which type of fail you have received, ask the tester to clarify before leaving.
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Common questions about what the MOT checks
What is the most common reason for an MOT fail?▾
Lights. Specifically, bulbs that have blown since the last test. This is also the cheapest fix. Before your MOT, walk around the car and check every light: headlights, brake lights, indicators, reverse lights, and the number plate light. Two minutes spent doing this can save a fail and a return trip.
Can I drive home if my car fails its MOT?▾
It depends on the type of failure. A major defect fail means the vehicle cannot be driven on public roads, but you can drive it directly to a pre-booked repair appointment or back home if that is where the repairs will happen. A dangerous defect fail means the vehicle should not be driven at all. Ask the tester which type of fail applies before you leave.
Do I have to use the same garage for repairs after a fail?▾
No. The tester gives you a VT30 listing the failures, and you can take that to any garage for repair. If you return to the original garage within 10 working days, you may qualify for a reduced partial retest fee covering only the failed items. If you go elsewhere or wait longer, you pay for a full new test.
What is an advisory and should I worry about it?▾
An advisory is a minor item flagged on a passed certificate. Your vehicle is road legal. The tester is telling you something is wearing or deteriorating and worth addressing before it becomes a fail. Common advisories include tyre wear approaching the legal limit, thin brake pads, or minor suspension wear. Act on it before next year's test. Sooner if it involves something safety-critical like brakes or tyres.
Are emissions tests the same for petrol and diesel vehicles?▾
No. Petrol vehicles are assessed using a gas analyser measuring carbon monoxide, hydrocarbons, and the air-fuel mixture (lambda). Diesel vehicles are tested using a free-acceleration smoke test, where exhaust opacity is measured as the engine is revved sharply. The pass standards differ by fuel type. Tampering with or removing a diesel particulate filter (DPF) is an automatic fail.
Can a nearly-new car fail its MOT?▾
Yes. A vehicle under three years old does not need an MOT at all, but once it does, age is no protection. A newer vehicle with a faulty headlight, a damaged tyre, or an emissions fault will fail. In practice, newer vehicles rarely fail for structural or wear-related reasons. Most failures on younger cars are straightforward items like a blown bulb.
What is a dangerous defect?▾
A dangerous defect is an immediate risk to road safety. It causes a fail, and the vehicle should not be driven until fixed. Not even to a repair garage. Examples include a steering failure, severe brake deficiency, or structural damage that compromises crash protection. Most MOT failures are major defects, not dangerous ones. If your fail certificate includes a dangerous defect, arrange collection or recovery rather than driving away.
Does the MOT test the spare tyre?▾
No. Only the four fitted tyres are inspected as part of the MOT. The spare tyre is not tested.